In recent years, a taste sensor device with lipid molecular films and a taste sensing system using the device have been developed as a taste recognition apparatus and a taste recognition system using the apparatus. The device and the system are capable of detecting, evaluating by quantifying the taste of food or the like and visually displaying the detection result on a graph or the like using a taste sensor with lipid molecular films of an amphiphatic substance or a bitter substance, for example, as a replacement of gustation, one of the five senses of the human being.
Patent Document 1, Patent Document 2, Patent Document 3 and Patent Document 4 described later are known, for example, as patents granted to Anritsu Co., Ltd. et al. who have transferred the business thereof to the present applicant or the assignee thereof with regard to the aforementioned taste sensing system with lipid molecular films.
All the patent rights on the taste sensing system with lipid molecular films including those of Patent Documents 1 to 4 are assigned to the present applicant or the assignee of this application from Anritsu Co., Ltd.
In order to facilitate the understanding of this invention, the gist of the contents of Patent Documents 1 to 4 will be briefly explained below.
First, Patent Document 1 filed earliest of all the cited patent documents indicates that lipid molecular films constitute a taste sensor adapted to work as a replacement of human taste. Each of lipid molecular films has a structure in which a lipid substance (of which the amphiphatic substance is a kind) with molecules having both a hydrophobic portion and a hydrophilic portion is fixed in a high-polymer matrix and the hydrophilic portion is aligned on the surface thereof. Patent Document 1 also discloses a specific taste sensing system using the taste sensor.
FIG. 20 is a diagram, shown by an expression method used to design chemical substances, for explaining a model of the lipid molecular films disclosed in Patent Document 1 as a conventional taste recognition apparatus.
In FIG. 20, spherical portions of the lipid molecules indicated by circles each designate a hydrophilic group a, i.e. a hydrophilic portion a from which a long chain structure b (such as an alkyl group) of hydrocarbon extends as an atomic arrangement.
In all cases shown in FIG. 20, two chains extend as one molecule and a molecule group is formed by the molecules as a whole. The portion of hydrocarbon in chain form constitutes a hydrophobic portion b.
This lipid molecule group 31 is accommodated in a matrix 33 (surface structure or a micro structure having a planar expansion), though partly penetrated into the matrix (for example, designated by reference numeral 31′ in FIG. 20), on the surface of a film member 32. The lipid molecule group 31 is thus accommodated with the hydrophilic portion arranged on the surface.
FIG. 21A is a sectional view shown for explaining three sensory units of an array electrode of a multi-channel taste sensor formed of the lipid molecular films disclosed in Patent Document 1 as a conventional taste recognition apparatus.
FIG. 21B is a plan view shown for explaining three sensory units of an array electrode of a multi-channel taste sensor formed of the lipid molecular films disclosed in Patent Document 1 as a conventional taste recognition apparatus.
In the case shown in FIGS. 21A, 21B, holes of 0.5 mmφ are formed through an acrylic base member 1, in which round silver rods are inserted as electrodes 2 each connected with a lead wire 5 by solder 6, while a lipid molecular film 3 is attached on the base member 1 in contact with the electrodes 2 through a buffer layer 4.
FIG. 22 is a block diagram shown for explaining a taste measurement system using the aforementioned multi-channel taste sensor disclosed in Patent Document 1 as a conventional taste recognition apparatus.
First, an aqueous solution of a sample substance is prepared and, as a sample solution 11, placed in a container 12 such as a beaker.
A taste sensor array 13 produced by arranging a lipid film and an electrode on the acrylic plate (base member) as described above is placed in the sample solution 11.
Before use, the electrode potential is stabilized with an aqueous solution of potassium chloride 1 mmol/l.
In FIG. 22, reference numerals 14-1, . . . , 14-8 designate the lipid films 3 as black points.
A reference electrode 15 is prepared for generating a reference potential for measurement, and placed in the sample solution 11.
The taste sensor array 13 and the reference electrode 15 are arranged in predetermined spaced relation with each other.
The surface of the reference electrode 15 is covered with a buffer layer 16 formed of potassium chloride 100 mmol/l solidified by agar. Therefore, the electrode system is configured of silver 2| silver chloride 4| lipid film 3 (14)| sample solution 12| buffer layer (potassium chloride 100 mmol/l) 16| silver chloride 4| silver 2.
The electrical signal from each lipid film 3 makes up 8-channel signals in FIG. 22, which are led by lead wires 17-1, . . . , 17-8 to buffer amplifiers 19-1, . . . , 19-8, respectively.
The outputs of the buffer amplifiers 19-1, . . . , 19-8 are selected by an analog switch (8 channels) 20 and applied to an analog/digital (A/D) converter 21.
The electrical signal from the reference electrode 15 is also applied to the A/D converter 21 through the lead wire 18, and the difference with the potential of the film is converted into a digital signal.
This digital signal is properly processed for the arithmetic operation required for taste measurement in a microcomputer 22 and displayed on an X-Y recorder 23.
In the case shown in FIG. 22, an 8-channel taste sensor is used, and the films used for each channel contains 11 types of lipid molecular film, as shown below, having different taste response characteristics to obtain taste information sufficiently great in amount to reproduce the human taste.
No.Lipid substance1Dioctyl phosphate2Cholesterol3Trioctylmethyl ammonium chloride4Oleic acid5n-octadecyl chloride6Diphenyl phosphate7Decyl alcohol8Dioctadecyl dimethyl ammonium bromide9Lethicin10Trimethyl stearyl ammonium chloride11Oleyl amine
The taste sensor described in Patent Document 1, which is a taste sensor in the true sense of the words, has the physicochemical quality similar to the tongue, i.e. the gustatory organ of the human being, and can produce a similar output for a similar taste in spite of a different sample substance while at the same time producing some output for a different taste.
Next, Patent Document 2 discloses a method of detecting the taste using the taste sensor described in Patent Document 1.
The invention relating to the taste detection method disclosed in Patent Document 2 makes it possible to identify even the delicate difference in taste such as the brand difference and the lot difference of beer and other foods. This taste detection method will be described briefly below.
Specifically, according to this taste detection method, a reference liquid similar to a sample liquid is used to secure a high reproducibility for detection and measurement of the taste by the taste sensor using lipid molecular films.
The taste sensor is dipped sufficiently in this reference liquid, and a similar stimulus is applied for each measurement using the taste sensor.
The time of measurement is selected at an appropriate time when the internal potential slowly changes after stabilization of the surface potential, and the difference in the measurement value between the reference liquid and the sample liquid is calculated.
In the case where the sample is beer, the beer or a substance similar to the beer is used as a reference liquid. The taste sensor is dipped in this reference liquid in advance and familiarized with the reference liquid.
As a result, an adsorptive substance is adsorbed in advance to the lipid film contained in the beer, and therefore, the effect of the adsorptive substance on the measurement of various types of beer is reduced.
This taste detection method has the advantage that the reproducibility is highly improved although the sensitivity to a substance having the adsorptive property to the lipid film is reduced.
Next, Patent Document 3 discloses a taste detection method advanced from the method for detecting the taste using the taste sensor described in Patent Document 2.
In the taste detection method according to a first aspect of the invention disclosed in Patent Document 3, in order to carry out the taste detection and measurement with a high reproducibility by the taste sensor using the molecular film of the amphiphatic or bitter substance containing the lipid film described above (hereinafter briefly referred to as the molecular film), a first reference liquid and a second reference liquid similar to the sample liquid are used. Then, by calculating the value ((Vs−V0′)−(Vk−V0)) relative to the reference value of the sample liquid measurement taken for the first reference liquid (V0), the second reference liquid (Vk), the first reference liquid (V0′) and the sample liquid (Vs) in that order, the variation in the relative value in the sustained drift of the taste sensor is eliminated. At the same time, by using the first reference liquid, the effect on the measurement value can be eliminated even in the case where the taste of the first reference liquid undergoes a change.
In the case where the taste of the sample solution containing an adsorptive substance is measured using the taste sensor having the molecular film of an amphiphatic or bitter substance as described above, a first measurement value obtained by the taste sensor with no adsorptive substance adsorbed to lipid molecular films is different from a second measurement value obtained by the taste sensor with the adsorptive substance adsorbed to lipid molecular films. Although the difference is gradually decreased, the measurement value is different between the second and third measurement sessions, between the third and fourth sessions, and so forth.
In such a case, the adsorptive substance should better be removed from the molecular film. For lack of the proper method of removal, however, the measurement of the sample solution containing the substance adsorptive to the molecular film is conducted by the taste sensor using the molecular film in such a manner that before measurement of the sample solution, a reference liquid having components similar to the sample solution is prepared, and by sufficiently dipping the taste sensor in the reference liquid, the substance adsorptive to the molecular film in the reference liquid is adsorbed in advance.
By doing so, this taste detection method reduces (stabilizes) the effect of the adsorptive substance at the time of measurement and thereby improves the reproducibility.
According to the taste detection method described in Patent Document 3, in order to improve (stabilize) the reproducibility, the taste sensor is sufficiently dipped in a liquid having a similar component to the sample solution as a pre-measurement stage, and the substances adsorptive to the film (lipid molecular film) are adsorbed in advance of measurement. (1) This poses the problem, therefore, that the sensitivity to a sample substance such as bitterness high in adsorption is reduced.
Regardless of adsorption of an adsorptive substance before measurement, a different type of lipid molecular films used for the taste sensor has a different amount of response to a basic taste such as sourness, saltiness, sweetness, bitterness or flavor.
Also, the lipid molecular films respond to a plurality of basic tastes. For example, a certain lipid molecular film responds not only to sourness but also to bitterness to one degree to another. Therefore, the ratio of response to each basic taste to the total response amount of a particular molecular film is unknown.
In addition, the advanced adsorption to an adsorptive substance makes the film surface of all the taste sensors become analogous to each other, and so the response to each basic taste becomes similar.
Thus, (2) the problem is posed that it becomes more difficult to decompose the response to each basic taste.
The aforementioned problems of the taste measurement method described in Patent Document 3 lead to the availability of a smaller amount of information on taste.
Next, Patent Document 4 discloses a taste measurement method for measuring the taste using a taste sensor with lipid molecular films which obviates the problems of the taste detection method for detecting the taste using the taste sensor described in Patent Document 3.
In the taste measurement method described in Patent Document 4, the desired reference liquid is prepared, a sensor potential V01 with a first reference liquid is measured, and the sensor is dipped for a predetermined time in a sample solution containing an ionizable adsorptive substance, after which a sensor potential V02 in a second reference liquid is measured and the difference is determined between V01 and V02.
Also, in this taste measurement method, the second reference liquid is used which is lower in at least one of sourness and saltiness, i.e., at least 0.3 higher in pH hydrogen ion index (pH) and/or one half or lower in electric conductivity than the first reference liquid.
Also, in this taste measurement method, the taste sensor is cleaned before measuring the sensor potential V02 with the second reference liquid, for example.
With any desired reference liquid described above containing no ionizable adsorptive substance, any sample solution is measurable.
This is because, in such a reference liquid, no ionizable adsorptive substance is adsorbed to the molecular film when the taste sensor is dipped in it.
An aqueous solution containing only acid and/or salt and such an aqueous solution with a sweet flavor added thereto are some examples.
A reference liquid containing the same ionizable adsorptive substance as the sample solution in such a small amount as not to affect the taste measurement of the sample solution can be employed.
Even in the case where the ionizable adsorptive substance is adsorbed to the molecular film with the taste sensor dipped in the reference liquid, no problem is posed as long as the amount so adsorbed is ignorable as compared with the amount adsorbed when dipped for a predetermined time in the sample solution.
In the taste measurement method described above, the sensor potential of the first reference liquid is set to V01 and the sensor potential of the second reference liquid after dipping in the sample solution (sample liquid) to V02.
In the absence of an ionizable substance adsorptive to the molecular film in the sample liquid, V02 is substantially equal to V01.
To simplify the description below, the first and second reference liquids are assumed to contain the same components.
In the presence of an ionizable substance adsorptive to the molecular film, on the other hand, the ionizable adsorptive substance adsorbed to the surface of the molecular film works as a fixed charge of the molecular film. The film potential changes with the density of the fixed charge.
Even in the case where the same reference liquid is measured, the film potential is varied between the cases in which an ionizable adsorptive substance is adsorbed and not adsorbed to the surface of the molecular film, and therefore, V01 and V02 are different from each other.
The difference between V01 and V02 corresponds to the amount of adsorption of the ionizable adsorptive substance to the film.
The time for dipping in the sample solution being constant, the amount of adsorption of an ionizable adsorptive substance to the film corresponds to the density of the ionizable adsorptive substance contained in the sample solution. By measuring V01, V02 and determining the difference therebetween, therefore, the information on the taste presented by the ionizable adsorptive substance of the sample solution is obtained.
Also, by employing a liquid weaker in taste than the first reference liquid as a second reference liquid, the measurement sensitivity is improved.
In other words, even in the case where the measurement of two sample liquids shows the same difference of the amount adsorbed to the film, the difference in measurement value is larger in the case where the second reference liquid is weaker in taste than the first reference liquid.
In the case where the taste sensor is cleaned before measuring the sensor potential V02 with the second reference liquid, only a substance adsorbed with not less than a certain level of strength is left and the taste information on the remainder can be obtained by selecting the degree of strength of cleaning, the type of cleanser, etc.
Next, a taste recognition system to which the taste measurement method described in Patent Document 4 is applied will be briefly explained.
A batch-type taste recognition system as shown in FIGS. 23 to 27A, 27B includes a detector/handler unit 101 and a data processing unit 102.
FIG. 23 is a perspective view shown for explaining the configuration of the batch-type taste recognition system disclosed in Patent Document 4 as a conventional taste recognition apparatus.
As shown in FIG. 23, the detector/handler unit 101 includes a measurement table 101a, a robot proper 101b, a robot drive unit 101c and a container mounting plate 101d. 
A sensor unit 101e is mounted at the forward end of the robot proper 101b. 
FIG. 24 is a perspective view shown for explaining the configuration of the sensor unit 101e of the batch-type taste recognition system disclosed in Patent Document 4 as a conventional taste recognition apparatus.
The sensor unit 101e, as shown in FIG. 24, includes a buffer amplifier 101f, a sensor support unit 101g, a sensor guard 101h, a photosensor 101i, a plurality of sensor probes 101j and a reference electrode 101k. 
FIG. 25A is a side view shown for explaining the configuration of the sensor probes 101j of the sensor unit 101e in the batch-type taste recognition system disclosed in Patent Document 4 as a conventional taste recognition apparatus.
FIG. 25B is a side view shown for explaining the configuration of the reference electrode 101k of the sensor unit 101e in the batch-type taste recognition system disclosed in Patent Document 4 as a conventional taste recognition apparatus.
The sensor probes 101j and the reference electrode 101k, as shown in FIGS. 25A, B, each include a probe proper 1011, an electrode terminal 101m, an Ag/AgCl electrode 101n and an internal liquid (saturated AgCl, 3.3 MKCl) 101o. 
A lipid substance film 101p is arranged at the forward end of each sensor probe 101j. 
A saturated KCl agar 101q is arranged at the forward end of the reference electrode 101k. 
The data processing unit 102 includes a rack proper 102a, a power supply box 102b, a personal computer 102c, an operation unit 102d and a display unit 102e. 
FIG. 26 is a block diagram shown for explaining the configuration of the control system of the batch-type taste recognition system disclosed in Patent Document 4 as a conventional taste recognition apparatus.
FIG. 27A is a perspective view shown for explaining automatic measurement conducted by dipping the sensor unit 101e in a reference liquid container, a passivation liquid container, a cleanser container and a measurement liquid (sample liquid) container mounted in a predetermined form on the container mounting plate 101d of the batch-type taste recognition system disclosed in Patent Document 4 as a conventional taste recognition apparatus.
Incidentally, FIG. 27A shows the automatic measurement conducted by using a sample cleanser with the passivation liquid and the reference liquid being different from each other.
FIG. 27B is a perspective view shown for explaining the automatic measurement conducted by dipping the sensor unit 101e in the reference liquid container, the passivation liquid container, the cleanser container and the measurement liquid (sample liquid) container mounted in a predetermined form on the container mounting plate 101d of the batch-type taste recognition system disclosed in Patent Document 4 as a conventional taste recognition apparatus.
Incidentally, FIG. 27B shows the automatic measurement conducted without using the sample cleanser with the passivation liquid and the reference liquid being identical with each other.
In the batch-type taste recognition system having this configuration, as shown in FIG. 26, the automatic measurement is conducted with the robot proper 101b of the detector/handler unit 101 controlled by the personal computer 102c while the sensor unit 101e is dipped in the reference liquid container, the passivation liquid container, the cleanser container, the measurement liquid (sample liquid) container and the like mounted in a predetermined form on the container mounting plate 101d, as shown in FIGS. 27A, B.
The data processing unit 102, with the data from the sensor unit 101e subjected to A/D conversion and fetched into the personal computer 102c for analysis of the main component, finally recognizes the taste of the sample liquid and outputs the taste information.
Under the circumstances, however, even the taste sensing system with lipid molecular films as the conventional taste recognition apparatus and the taste recognition system using the apparatus developed through the process as disclosed in Patent Documents 1 to 4 described above still encounter many problems to be solved as described below.
Desirably, for example, in the taste sensing system with lipid molecular films as viewed from the operator as a user, the taste of a sample substance can be measured with a simple operation while at the same time making it possible to easily analyze and evaluate the taste measurement result following a procedure in which it is easy to understand what is going on.
Also, the taste sensing system with lipid molecular films as viewed from the operator as a user has preferably such a high maintainability that the point of a trouble, if any occurs, can be grasped and solved easily.
Further, from the viewpoint of the user as a quality controller of the sample taste substance, the taste sensing system with lipid molecular films desirably has the operating ease with which the taste measurement can be readily conducted individually by a normal operator at a plurality of points on the production line. At the same time, a simple network is desired for collective centralized management of the analysis and evaluation data on the individual taste measurement results at a management center terminal.
In spite of a version-up, if any, of the OS of the personal computer used as a terminal, the correction of the software of the taste sensing system with lipid molecular films is desirably not required.
Also, it is desired from the viewpoint of the user as a quality controller of the sample taste substance that the efficient maintenance for the taste sensing system with lipid molecular films can be conducted using a network.
Also, what is desired by a researcher as a user of the taste sensing system with lipid molecular films is a superior function with a sophisticated analytical ability satisfactory for research purposes, while the operation thereof is easy even for laboratory assistants.
In this case, the taste sensing system with lipid molecular films as viewed from a commodity planning division as a user desirably has the appropriate ability to express the matters related to quality control as a commodity of which the analysis result can be used for marketing.
Specifically, in the taste sensor apparatus with lipid molecular films and the taste sensing system using the apparatus, which make up the aforementioned taste recognition apparatus and the taste recognition system using the apparatus as a whole, it is desirable that the taste of the sample taste substance can be measured with a simpler operation and the result of the taste measurement can be easily analyzed and evaluated while at the same time securing a high maintainability.
Patent Document 1: U.S. Pat. No. 5,482,855 (corresponding to JP 2,578,370, EP 410,356)
Patent Document 2: U.S. Pat. No. 5,302,262 (corresponding to JP 3,037,971, EP 464,820)
Patent Document 3: JP 3,313,433
Patent Document 4: U.S. Pat. No. 5,789,250 (corresponding to JP 3,547,760, EP 763,729)